3
Wanted: Long-Term Roommate; Must Help Keep House and Have Own DNA Only a fraction of the cells in our bodies are our own Parasites and microbes make up the remainder of our body composition The evolution of eukaryotes is closely linked to their relationship with prokaryotes

4
Certain Large Biomolecules are Common to All Life-Forms The cell is the smallest and simplest unit of life Prokaryotes differ from eukaryotes in several key characteristics Internal structures enable cells to function as an efficient and well-coordinated unit

5
Cells: The Smallest Units of Life The cell theory is a unifying principle of biology The cell theory is based on two concepts: – Every living organism is composed of one or more cells – All cells living today came from a preexisting cell A cell is composed of an aqueous interior enclosed in a lipid-based plasma membrane

6
Cells: The Smallest Unit of Life Cytoplasm contains a thick fluid called cytosol, consisting of ions and biomolecules mixed in water An organelle is a cytoplasmic structure that performs a unique function in the cell The nucleus contains the DNA enveloped in double membranes The mitochondrion (plural: mitochondria) provides the energy that fuels all cellular functions Ribosomes are important protein-manufacturing organelles

7
Cells: The Smallest Unit of Life Cells have many different shapes, sizes, life strategies, and behaviors Prokaryotes are generally single-celled organisms All members of the plant and animal kingdom are multicellular

8

9
The Microscope Is a Window into the Life of a Cell The light microscope was the first instrument that enabled scientists to view the cell Electron microscopes use streams of electrons focused with magnets to magnify specimens more than 100,000 times A scanning electron microscope creates a three-dimensional view of specimen

10

11

12

13
The Ratio of Surface Area to Volume Limits Cell Size Most cells are microscopic and cannot be seen with the naked eye Prokaryotic cells are generally smaller than eukaryotic cells Cell size is limited in order to maintain a ratio of surface area to volume that allows the cell to efficiently exchange materials with the environment

14

15
Multicellularity Enables Larger Body Size and Efficiency through Division of Labor A multicellular organism consists of an interdependent group of genetically identical cells that developed from a single cell and whose cells are incapable of living independently Colonial organisms consist of a loose group of cells that cooperate for mutual benefit but can also exist independently

16

17
Multicellularity Enables Larger Body Size and Efficiency through Division of Labor Multicellularity makes cell specialization possible and enables the individual to function more efficiently through division of labor Multicellular organisms have different cell types that share the same DNA but express different subsets of DNA information, giving the cells different skill sets

18

19
The Plasma Membrane Every cell has a plasma membrane that separates the cell from its surrounding environment The plasma membrane acts to facilitate chemical processes by concentrating the needed raw materials in a limited space

20
The Plasma Membrane The plasma membrane is a selectively permeable barrier that is responsible for the following: – Capturing needed molecules and bringing them into the cell – Removing waste from the cell – Communicating with other cells and the environment – Anchoring the cell in place

21
The Plasma Membrane Proteins embedded in the phospholipid bilayer are responsible for the diverse functions carried out by plasma membrane and include: – Transport proteins – Receptor proteins – Adhesion proteins The fluid mosaic model of the plasma membrane allows the proteins to drift within the plane of the phospholipid bilayer

22

23
Prokaryotic and Eukaryotic Cells Most prokaryotes have a tough cell wall outside the plasma membrane Some bacteria have a slippery, protective layer called a capsule Eukaryotes are characterized by membrane- bound organelles that confer speed and efficiency through intracellular division of labor

24

25

26
Internal Compartments of Eukaryotic Cells Eukaryotic cells are highly structured, efficient, energy-dependent factories that have the capacity to reproduce themselves All living creature are vastly more complex than any man-made machine

27
The Nucleus Houses Genetic Material In eukaryotic cells, the nucleus in bound by a double plasma membrane called the nuclear envelope The nucleus contains the DNA required for building, managing, growing, and reproducing all cells Each DNA double helix is condensed into chromosomes

28
The Nucleus Houses Genetic Material The nuclear envelope contains nuclear pores through which ions and small molecules pass freely Passage of larger molecules and proteins is regulated by the nuclear pores RNA is used to carry directions for making proteins to the ribosomes

29

30
The Endoplasmic Reticulum Manufactures Certain Lipids and Proteins The endoplasmic reticulum (ER) is an interconnected network of tubes and flattened sacs that produces certain lipids and proteins Enzymes of the smooth ER produce lipids for other cellular compartments and help break down toxic organic compounds in the cell The rough ER is dotted with ribosomes that produce proteins for use both inside and outside the cell

31

32
Transport Vesicles Move Materials A transport vesicle is a small, spherical, membrane-enclosed sac that moves lipids, proteins, and carbohydrates between cellular compartments The transport vesicle fuses with the membrane of the target destination in order to deliver its contents

33

34
The Golgi Apparatus Sorts and Ships Macromolecules The Golgi apparatus directs proteins and lipids produced by the ER to their final destination, either inside or outside the cell, through the addition of specific chemical groups Vesicles move the lipids and proteins from the ER to the Golgi apparatus

35

36
Lysosomes and Vacuoles Disassemble Macromolecules Lysosomes use a variety of enzymes to break down macromolecules and release the subunits into the cytoplasm for recycling or waste removal The interior of lysosomes is highly acidic, with a pH of about 5

37

38
Lysosomes and Vacuoles Disassemble Macromolecules Plant organelles called vacuoles act much like lysosomes to break down macromolecules Vacuoles can also store ions and water-soluble molecules as well as noxious compounds, which deter herbivores Vacuoles filled with water provide turgor pressure, which helps make the nonwoody parts of plant cells rigid

39

40
Mitochondria Power the Cell The mitochondrion fuels cellular activities by extracting energy from food molecules Plant cells have an additional organelle called the chloroplast, which uses sunlight to make energy-storing molecules The mitochondrion is bound by double membranes that form an intermembrane space

41
Mitochondria Power the Cell The folds of the inner membrane form the cristae, which help to increase the surface area for chemical reactions Mitochondria use chemical reactions to turn food molecules into ATP, which can be used to fuel the chemical reactions of the cell The process of turning food molecules into energy is called cellular respiration

42

43
Chloroplasts Capture Energy from Sunlight Plants and algae use chloroplasts to capture energy from sunlight to produce ATP The ATP is then used to assemble sugar molecules from carbon dioxide and water in a process called photosynthesis The energy in plant sugars is used directly by plants and indirectly by all organisms that eat plants Oxygen is a by-product of photosynthesis and sustains life for humans and many other organisms

44

45
The Cytoskeleton The interior of a cell is organized by a network of protein cylinders and filaments called the cytoskeleton The cytoskeleton supports the movement of organelles, strengthens cell membranes, and can even enable cell movement, and contains: – Microtubules – Intermediate filaments – Microfilaments

46

47
The Cytoskeleton Consists of Three Basic Components Microtubules are rigid, hollow cylinders of protein used for: – Positioning organelles – Moving transport vesicles and other organelles – Generating force to propel the cell Intermediate filaments are ropelike cables of protein that provide mechanical reinforcement to the cell Microfilaments are thin, flexible proteins that create cell shape and generate crawling movements in some cells

48

49
Microtubules Support Movement inside the Cell Microtubules are made of protein subunits called tubulin Most cells have a radial pattern of microtubules, which acts as a scaffold that helps position organelles within the cytosol Microtubules can act as a rail system to guide organelles to their destination within the cell

50
Intermediate Filaments Provide Mechanical Reinforcement Intermediate filaments are thinner than microtubules and provide structural and mechanical support The nuclear membrane is supported by intermediate filaments

51
Microfilaments Are Involved in Cell Movement Microfilaments are thin strands of protein called actin that can lengthen and shorten to create movement in a cell Cell crawling enables amoebas and slime molds to find food and mating partners Wound healing and embryonic development both rely on cell crawling

52

53
Cilia and Flagella Enable Whole Cell Movement Many protists and animals have cells covered in hairlike projections called cilia Cilia can be moved back and forth to move a whole cell through liquid Motor proteins interlinking the microtubules use ATP to cause the cilia to bend, causing the cell to move

54

55
Cilia and Flagella Enable Whole Cell Movement Some bacteria, archaeans, and protists and the sperm cells of some plants and animals use a flagellum (plural: flagella) to propel themselves through fluid Flagella are similar to cilia in structure Eukaryotic flagella differ from the flagella of prokaryotes in structure and movement

56

57

58
The Evolution of Eukaryotes Cells can exhibit mutualism when two cell merge Eukaryotic organelles are believed to have originally been free-living prokaryotes that were engulfed by a predatory cell